1. Field of the Invention
The invention relates to a hybrid switch which is connected between a power source and a load for conducting operations of making and breaking a current flowing through the load.
2. Background of the Invention
In such a hybrid switch, an electromagnetic contactor which is of a contact switch and a semiconductor switch device which is of a contactless switch are connected in parallel to each other, operations of making and breaking a current are conducted by the semiconductor switch, and a current flow after the current making operation is conducted through the electromagnetic contactor. According to the configuration where the semiconductor switch device conducts the current making and breaking operations and a current flows through the electromagnetic contactor, contacts of the electromagnetic contactor are prevented from being worn by arcs which may be generated between the contacts when the current making and breaking operations are conducted only by the electromagnetic contactor, whereby the life of the electromagnetic contactor can be prolonged.
In such a hybrid switch, an electromagnetic contactor and a semiconductor switch which are independently formed are individually mounted on a fixing frame, and they are connected to each other by using external wiring conductors. FIG. 10 is a connection diagram of a conventional hybrid switch of this kind.
In the figure, reference numeral 51 designates a power source for a main circuit, and 52 designates a load. A main circuit contact 53a which is driven by a magnetic coil 53 of an electromagnetic contactor is connected between the main circuit power source 51 and the load 52. Reference numeral 53b designates an auxiliary contact the operation of which is linked with that of the main contact 53a of the electromagnetic contactor. The auxiliary contact 53b is a normally closed contact which is closed when the main contact 53a is opened, and opened when the main contact 53a is closed. Reference numeral 54 designates a bidirectional triode thyristor which functions as a semiconductor switch device (such a thyristor is termed "triac" as a trade name of GE Co., and also in the specification such a thyristor is hereinafter called "triac"). The anode A and the cathode K are respectively connected to the both terminals of the main contact 53a in parallel, and the gate G is connected to one terminal of a resistor 55. The other terminal of the resistor 55 is connected to a junction of the anode A and one terminal of the main contact 53a. One terminal of the normally closed auxiliary contact 53b of the electromagnetic contactor is connected to a junction of the resistor 55 and the gate G of the triac 54, and the other terminal of the auxiliary contact to a junction of the cathode K of the triac 54 and the other terminal of the main contact 53a. In the figure, broken lines indicate, external wiring conductors.
The hybrid switch of FIG. 10 operates as follows: FIG. 10 shows a state where an operation voltage (not shown) is not applied to the magnet coil 53 of the electromagnetic contactor. In this state, the gate G and the cathode K of the triac 54 are short-circuited in the order of several milliohms by the normally closed auxiliary contact 53b. This allows a current from the resistor 55 to flow through the normally closed auxiliary contact 53b. Therefore, noises are prevented from entering the gate G so that the triac is not erroneously ignited. When the operation voltage is applied to the magnet coil 53 of the electromagnetic contactor in this state, the normally closed auxiliary contact 53b is opened before the main contact 53a is closed, and hence a voltage is applied across the gate G and the cathode K through the resistor 55 so that the triac 54 is immediately rendered conductive. After the triac 54 is turned on, the main contact 53a of the electromagnetic contactor is closed. During the period when the main contact 53a is closed, therefore, the voltage between the contact terminals of the main contact 53a is substantially zero. In other words, arcs are not generated between the contact terminals of the main contact 53a during the closed period of the main contact 53a. Since the voltage drop of the main contact 53a is very smaller than that of the triac 54 in the on-state, the current flow path after the main contact 53a is closed is changed from the triac 54 to the main contact 53a. Consequently, the triac 54 is requested only to allow a current to flow through it during a short period continuing until the main contact 53a is closed.
When the load current is to be interrupted, the application of the operation voltage to the magnet coil 53 is ceased. This causes the main contact 53a to be opened so that the load current is interrupted. During the very short period when the state of the main contact 53a is transferred from the close state to the open state, the normally closed auxiliary contact 53b is opened. Since a voltage is applied across the gate G and the cathode K, the flow path of the load current is changed to the triac 54. When the state of the main contact 53a is transferred to the open state, arcs are disposed to be generated between the contact terminals of the main contact 53a. Since the flow path of the load current is changed to the triac 54, no arc is generated between the contact terminals of the main contact 53a. Then, the normally closed auxiliary contact 53b is closed and the gate G and the cathode K of the triac 54 are short-circuited. At the instant when the load current (the current from the AC power source) is reduced to the zero level, the triac is turned off so that the load current is interrupted.
The conventional apparatus shown in FIG. 10 has such a structure that an electromagnetic contactor and a semiconductor switch which are independently formed are individually mounted on a fixing frame, and they are connected to each other by external wiring conductors. This structure suffers from defects such that a large area for installing both the electromagnetic contactor and the semiconductor switch is required, and that a cumbersome wiring work of connecting the electromagnetic contactor and the semiconductor switch by the external wiring conductors must be done. Moreover, the structure has a further drawback that, when the external wiring conductors are erroneously connected during such a wiring work, there occurs a trouble in the switching operation of the semiconductor switch.